Laser display system with optical feedback configured to reduce speckle artifacts

ABSTRACT

An imaging system ( 200 ) includes a plurality of laser sources ( 201 ) configured to produce a plurality of light beams ( 204 ). One or more optical alignment devices ( 220 ) orient the light beams ( 204 ) into a collimated light beam ( 205 ). A light modulator ( 203 ) modulates the collimated light beam ( 205 ) such that images ( 206 ) can be presented on a display surface ( 207 ). Speckle is reduced with an optical feedback device ( 221 ) that causes the laser sources ( 201 ) to operate in a coherence collapsed state. Examples of optical feedback devices ( 221 ) include partially reflective mirrors and beam splitter-mirror combinations.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.12/241,597, filed Sep. 30, 2008, which is incorporated herein byreference in its entirety for all purposes.

BACKGROUND

1. Technical Field

This invention relates generally to optical projection systemsconfigured to reduce perceived speckle, and more particularly to alaser-based system employing optical feedback in an external cavity tocause multiple lasers to operate in a coherence collapsed state, therebyreducing speckle as perceived by a viewer.

2. Background Art

Laser projection devices facilitate the production of brilliant imagescreated with vibrant colors. The image quality associated withlaser-based projection systems is unmatched by systems usingconventional projection devices. The advent of semiconductor lasers,such as laser diodes, allows these brilliant images to be created at areasonable cost, while using small amounts of power. Laser diodes aresmall, compact, and relatively inexpensive. Further, the light fromlaser diodes is easily modulated to form complex images.

One practical drawback associated with using lasers in projectionsystems is the image artifact known as “speckle.” Speckle occurs when acoherent light source is projected onto an imperfect projection medium.As the light is highly coherent, when it reflects off a rough surface,components of the light combine with other components to form patches ofhigher intensity light and lower intensity light. In a detector with afinite aperture, such as a human eye, these varied patches of intensityappear as speckles, as some small portions of the image look brighterthan other small portions. Further, this spot-to-spot intensitydifference can vary, which makes the speckles appear to move.

Turning now to FIG. 1, illustrated therein is a prior art system 100 inwhich an observer 101 may perceive speckle. Specifically, a coherentlight source 101, such as a semiconductor-type laser, delivers acoherent beam 104 to a modulation device 103. The modulation device 103modulates the coherent beam 104 into a modulated coherent beam 105capable of forming an image. This modulated coherent beam 105 is thendelivered to a projection medium, such as the projection screen 107shown in FIG. 1.

As the projection screen 107 is imperfect, i.e., as it includes tinybumps and crevices, the reflected light 108 has portions that combineand portions that cancel. As a result, the observer 102 views an image106 that appears to be speckled. The presence of speckle often tends toperceptibly degrade the quality of the image produced using the laserprojection system.

Numerous attempts have been made to control speckle. Prior art specklereduction systems include attempts to introduce angle diversity into thecoherent beam, attempts to introduce polarization diversity into thecoherent beam, attempts to introduce wavelength diversity into thecoherent beam, and so forth. Other devices employ diffusers, imagedisplacing devices, and other complex systems. Some speckle reductionsystems, such as those used with microscopes, employ long lengths ofoptical fiber in an attempt to stretch the projected light beyond acorresponding coherence length prior to delivering it to a user. Adrawback associated with each of these systems is that they addsubstantial cost and complexity to the overall system design. Forinstance, time-varying diffusers require moving or vibrating parts thatadversely affect the overall system size and complexity. Further, suchsystems tend to increase the power requirements of the overall system,thereby degrading efficiency.

There is thus a need for an improved speckle-reducing system for usewith laser-based projection systems such as those employingsemiconductor-type lasers.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIG. 1 illustrates a prior art laser-based projection system exhibitingspeckle characteristics.

FIG. 2 illustrates one embodiment of a speckle reduction system inaccordance with embodiments of the present invention.

FIG. 3 illustrates a spectral view of a semiconductor-type lasersuitable for use with embodiments of the present invention.

FIG. 4 illustrates a spectral view of a semiconductor-type laser beingdelivered a first amount of optical feedback in accordance with oneembodiment of the invention.

FIG. 5 illustrates a spectral view of a semiconductor-type laser beingdelivered a second amount of optical feedback in accordance with anotherembodiment of the invention.

FIG. 6 illustrates one embodiment of an imaging system configured toreduce speckle in accordance with embodiments of the invention.

FIG. 7 illustrates an alternate embodiment of an imaging systemconfigured to reduce speckle in accordance with embodiments of theinvention.

FIG. 8 illustrates one method of reducing speckle in accordance withembodiments of the invention.

FIG. 9 illustrates one sub-method step of the method of FIG. 8.

FIG. 10 illustrates one application for an imaging system in accordancewith embodiments of the invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments resideprimarily in combinations of method steps and apparatus componentsrelated to an imaging system configured to reduce perceived speckle.Accordingly, the apparatus components and method steps have beenrepresented where appropriate by conventional symbols in the drawings,showing only those specific details that are pertinent to understandingthe embodiments of the present invention so as not to obscure thedisclosure with details that will be readily apparent to those ofordinary skill in the art having the benefit of the description herein.

It will be appreciated that embodiments of the invention describedherein may be comprised of one or more conventional processors andunique stored program instructions that control the one or moreprocessors to implement, in conjunction with certain non-processorcircuits, some, most, or all of the functions of reducing speckle asdescribed herein. The non-processor circuits may include, but are notlimited to, microprocessors, scanning mirrors, image modulation devices,memory devices, clock circuits, power circuits, and so forth. As such,these functions may be interpreted as steps of a method to performspeckle reduction. Alternatively, some or all functions could beimplemented by a state machine that has no stored program instructions,or in one or more application specific integrated circuits, in whicheach function or some combinations of certain of the functions areimplemented as custom logic. Of course, a combination of the twoapproaches could be used. It is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such programs andcircuits with minimal experimentation.

Embodiments of the invention are now described in detail. Referring tothe drawings, like numbers indicate like parts throughout the views. Asused in the description herein and throughout the claims, the followingterms take the meanings explicitly associated herein, unless the contextclearly dictates otherwise: the meaning of “a,” “an,” and “the” includesplural reference, the meaning of “in” includes “in” and “on.” Relationalterms such as first and second, top and bottom, and the like may be usedsolely to distinguish one entity or action from another entity or actionwithout necessarily requiring or implying any actual such relationshipor order between such entities or actions. Also, reference designatorsshown herein in parenthesis indicate components shown in a figure otherthan the one in discussion. For example, talking about a device (10)while discussing figure A would refer to an element, 10, shown in figureother than figure A.

Embodiments of the present invention provide a multi-laser projectionsystem with speckle reducing components. The speckle reduction isperformed simply, in a low cost and efficient manner, by deliveringoptical feedback to the laser sources. The optical feedback firstdestabilizes the minimum linewidth mode of each laser source, andeventually results in coherence collapse when the amplitude of theoptical feedback amplitude reaches a threshold.

In one embodiment, a plurality of laser sources is configured to producea plurality of light beams. Optical elements, such as dichroic mirrors,are then used to orient each of these light beams into a collimated,coherent light beam. A modulation device, such as aMicroelectromechanical System (MEMS) scanning mirror, digital lightprojection (DLP) system, or other modulation device, modulates thecollimated, coherent light beam to present an image on a projectionmedium or display surface.

Speckle is reduced in embodiments of the invention via an opticalfeedback device, such as a partially reflective mirror, beamsplitter-mirror combination, or other device capable of separating thecollimated, coherent light beam into a projection component and afeedback component. The optical feedback device is disposed between thelaser sources and the modulation device, thereby defining an externalcavity with respect to each light source. The optical feedback devicedelivers the feedback component back to the laser sources, therebycausing each laser source to operate in a coherence collapsed state. Thecoherence collapsed state results in a projection beam that has abroader spectral width, which yields less perceived speckle. Embodimentsof the invention are small and compact, and are suitable for use asprojection systems in portable electronic devices.

Turning now to FIG. 2, illustrated therein is a general block diagram ofa speckle reducing laser imaging system 200 in accordance withembodiments of the invention. A plurality of laser sources 201 isconfigured to produce a plurality of light beams 204. In one embodiment,the plurality of laser sources 201 comprises a red laser, a blue laser,and a green laser. These lasers can be edge emitting lasers or verticalcavity surface emitting lasers. In one embodiment, each laser is asemiconductor laser that is small and efficient. Such lasers arecommonly available from a variety of manufacturers.

One or more optical alignment devices 220 are then used to orient theplurality of light beams 204 into a collimated light beam 205. Where theplurality of laser sources 201 comprise a red laser, blue laser, andgreen laser, the one or more optical alignment devices 220 can blend theoutput of each laser to form a coherent beam of white light. In oneembodiment, dichroic mirrors can be used to orient the plurality oflight beams 204 into the collimated light beam 205. Dichroic mirrors arepartially reflective mirrors that include dichroic filters thatselectively pass light in a narrow bandwidth while reflecting others.Dichroic mirrors and their use in laser-based projection systems areknown in the art.

A light modulator 203 is then configured to produce images 206 bymodulating the collimated light beam and delivering it to a displaysurface 207. In one embodiment, the light modulator 203 comprises a MEMSscanning mirror. Examples of MEMS scanning mirrors, such as thosesuitable for use with embodiments of the present invention, are setforth in commonly assigned, copending U.S. patent application Ser. No.11/775,511, filed Jul. 10, 2007, entitled “Substrate-Guided Relays forUse with Scanned Beam Light Sources,” which is incorporated herein byreference, and in US Pub. Pat. Appln. No. 2007/0159673, entitled,“Substrate-guided Display with Improved Image Quality,” which isincorporated herein by reference. Embodiments of the invention are wellsuited for use with MEMS scanning mirrors as the overall system can bedesigned with a very small form factor, suitable for use in portableelectronics such as mobile telephones, personal digital assistants,gaming devices, music players, multimedia devices, and so forth.However, it will be clear to those of ordinary skill in the art havingthe benefit of this disclosure that other light modulators, such asdigital light projection modulators, may be used as well.

To reduce perceived speckle, an optical feedback device 221 is disposedbetween the plurality of laser sources 201 and the light modulator 203.In one embodiment, the optical feedback device 221 is disposed betweenthe light modulator 203 and the one or more optical alignment devices220. The optical axis running from the plurality of laser sources 201and the optical feedback device 221 defines an external cavity 224 foreach laser source. The optical feedback device 221 delivers a feedbackcomponent 222 to the plurality of laser sources 201, while delivering aprojection component 223 to the light modulator 203. The feedbackcomponent 222 has amplitude sufficient to cause each of the plurality oflaser sources 201 to operate in a state of coherence collapse. Coherencecollapse causes considerable broadening of the spectral linewidth of thelasing modes of each of the plurality of laser sources 201. This reducesspeckle appearing when images 206 from the light modulator 203 aredisplayed on the display surface 207. In effect, embodiments of thepresent invention exploit the coherence collapse phenomenon to suppressspeckle effects in laser projection systems.

The external cavity 224, which gives rise to the coherence collapse ofeach laser source, is defined by the optical path length between thefacets of each of the plurality of laser sources 201 to the opticalfeedback device 221. The length of this external cavity 224 may beselected such that the desired linewidth broadening of each laser sourceis insensitive to external cavity phase, i.e., sub-wavelength changes inthe external cavity length. In one embodiment, the length of theexternal cavity 224 is chosen to be greater than the length below whichthe coherence collapse effect is not observed.

In one embodiment, the length of the external cavity 224 is selected tobe an order of magnitude greater than the cavity length of each of thelaser sources and less than the characteristic coherence length of eachlaser. For example, when using a red laser, blue laser, and green laseras the plurality of laser sources 201, the red laser may have a cavitylength of roughly 1 millimeter, as will the blue laser. The green lasergenerally has a longer cavity length, such as 3-4 millimeters. Thecoherence length of each laser can run from several centimeters tohundreds of meters, but will often be on the order of tens ofcentimeters to a meter. Thus, the length of the external cavity 224 maybe selected to be, for instance, about 10 millimeters long, which isgreater than the cavity length of each laser source but less than thecoherence length of the laser sources without feedback. In oneembodiment of the invention, the length of the external cavity isbetween 0.1 and 100 millimeters.

The amplitude of the feedback component 222 is selected to be greaterthan that which is needed to destabilize the minimum linewidth mode ofeach laser. Such feedback begins to excite multiple modes in each lasersource, with each of these multiple modes being separated by arelaxation oscillation frequency corresponding to the laser. As theamplitude of the feedback component 222 reaches a threshold, each lasersource is driven into coherence collapse, thereby considerablybroadening the spectral linewidth of each source. This broadeningreduces speckle seen by a viewer.

In practice, the amount of feedback can be determined for a particularsystem or a particular manufacturer's laser diodes by employing avariable optical feedback device to tune the optical feedback to anamount sufficient to drive each of the plurality of laser sources 201into coherence collapse. Once the proper amount of feedback is known, asystem can be designed with a fixed optical feedback device having thedesired reflectivity. The amount of feedback is at least enough as todestabilize a minimum linewidth mode of each of the laser sources.Experimental calculations based upon research show feedback havingamplitude of approximately five percent of that of the collimated lightbeam 204 will cause sharp broadening in linewidth of each of theplurality of laser sources 201 due to the coherence collapse phenomenon.The coherence collapse phenomenon will be illustrated in more detail inFIGS. 3-5.

Turning now to FIG. 3, illustrated therein is a laser source 301 and agraph of its characteristic output 330 when no optical feedback isapplied. The laser source 301 has an internal cavity length and acoherence length associated therewith. Where the laser source is a redlaser, the cavity length may be on the order of 1 millimeter, while thecoherence length may be between 10 and 100 centimeters.

The characteristic output 330 of the laser source is centered about arelaxation oscillation frequency 331 and has a spectral linewidth 332.For a typical semiconductor laser available from a given vendor, thisspectral linewidth 332 may be roughly 10 MHz.

Turning now to FIG. 4, illustrated therein is the laser source 301having an optical feedback device 421 configured to deliver a feedbackcomponent 422 to the laser source 301 while delivering a projectioncomponent 423 to a light modulator 403 in accordance with embodiments ofthe invention. The amplitude of the feedback component 422 is relativelysmall, such as a few percent of the amplitude of the laser source'soutput. The amplitude of the feedback component 422 is sufficient as todestabilize the minimum linewidth mode of the laser source 401. As such,the output 430 of the system is a plurality of excited modes that areseparated by the relaxation oscillation frequency of the laser source301.

Turning now to FIG. 5, illustrated therein is the system of FIG. 4, withthe amplitude of the feedback component 422 increased to around fivepercent of the amplitude of the laser source's output. The multi-modeoutput (430) of FIG. 4 has now become an output 530 in a coherencecollapsed state. The initial spectral linewidth (332) of 10 MHz has nowspread into a spectral linewidth of between 10 and 20 GHz. Thisbroadening of the spectral linewidth reduces the combinative effects oflight reflecting from a display surface (207), thereby reducing speckle.

Operational states of coherence collapse are often avoided in industrybecause such states cause the relative intensity noise to increasedramatically. However, while the increase in relative intensity noisemay be deleterious in applications such as optical communicationsystems, it does not degrade performance of embodiments of the presentinvention. Applications for embodiments of the present invention, suchas projection display applications, do not suffer from increases inrelative intensity noise because detectors such as the human eye averagethis increased noise. As a result, projected images in accordance withembodiments of the present invention suffer no adverse image qualityeffects from increased relative intensity noise. Further, any increasednoise may average out image artifacts caused by laser self-heating andother operational characteristics.

Additionally, some prior art speckle reduction systems have attempted touse the “multi-mode” state of operation shown in FIG. 4 to reducespeckle. However, such prior art systems generally require postmodulator radiation alteration. For example, prior art solutions inmicroscopes employ a single laser light source and then use extensivelengths of fiber optic cable in an attempt to deliver light at adistance from the source that exceeds the coherence length of the lasersource. Embodiments of the present invention are not only able to usemultiple laser light sources, but have no need for post modulatorradiation alteration as each laser is drive into coherence collapse.

Turning now to FIG. 6, illustrated therein is one embodiment of a lightprojection source 600 in accordance with embodiments of the invention.Three laser light sources 661,662,663 are oriented so as to produce aplurality of light beams 604. Each laser light source 661,662,663 has acharacteristic minimum linewidth mode and a coherence length associatedtherewith. In one embodiment, the laser light sources 661,662,663comprise a green laser light source, a red laser light source, and ablue laser light source. In one embodiment, each laser light source661,662,663 comprises a semiconductor laser source suitable for mountingon a printed wiring board or other substrate.

A plurality of optical alignment 664,665,666 is configured to directoutput light from each of the laser light sources 661,662,663 along anoptical axis 667 as a coherent, collimated light beam. In theillustrative embodiment of FIG. 6, the plurality of optical alignmentdevices 664,665,666 each comprise dichroic mirrors. It will be clear tothose of ordinary skill in the art having the benefit of this disclosurethat other optical alignment devices configured to direct multiple lightbeams into a single collimated light beam may also be used.

A light modulator 603 receives the collimated light and modulates it soas to produce images suitable for projection onto a display surface(207). In the illustrative embodiment of FIG. 6, the light modulator 603comprises a MEMS scanning mirror 668. A partially reflecting mirror 669directs the collimated light to the MEMS scanning mirror 668. As notedabove, other light modulating devices, such as digital light projectionsystems, may be used in place of the MEMS scanning mirror 668. Anadvantage of the MEMS scanning mirror 668 is that it facilitates a verysmall, efficient light projection source 600.

An optical feedback component 621 is then configured to reflect afeedback component of light along the optical axis 667 to the threelaser light sources 661,662,663, thereby causing destabilization andspreading of each minimum linewidth mode. In one embodiment, theamplitude of the feedback component is selected so as to drive each ofthe three laser light sources 661,662,663 into a coherence collapsedstate.

In the illustrative embodiment of FIG. 6, the optical feedback component621 comprises a mirror having a partially reflective coating. Partiallyreflective coatings are generally known to those of ordinary skill inthe art. Such coatings can be used to reflect some components ofincident light and transmit others. Further, such coatings can be usedtransmit or reflect certain levels of light, or amounts of light thatdepend upon polarization. These coatings can be metallic layers—such asthin layers of silver. Alternatively, they may be multi-layer structuresdeposited by a vapor deposition process or other suitable manufacturingprocess. Additional details about the construction of suitable partiallyreflective coatings may be found in application Ser. No. 11/603,964,entitled “Substrate-Guided Display with Improved Image Quality,” filedNov. 21, 2006 and incorporated by this reference in its entirety.

Some coatings can be configured to preferentially reflect incident raysacross a particular range of angles. For example, several monolithiclayers of partially reflecting material can be configured to exhibit apolarization preference, and angle preference, or a combination thereof.Alternatively, separate angle preferential and polarization preferentialpartial reflective layers may be used, with each layer contributing aportion of the reflected energy.

In one embodiment, the partially reflective coating on/in the opticalfeedback component 621 is configured to reflect between one and tenpercent of the combined light beam coming from the plurality of opticalalignment devices 664,665,666. In one embodiment, the partiallyreflective coating comprises a multi-layer coating. For example, thepartially reflective coating can be configured to deliver feedbackcorresponding with a respective spectral width of each laser lightsource 661,662,663. By delivering the optical feedback, each laser lightsource 661,662,663 is driven into coherence collapse, thereby reducingperceived speckle from the light projection source 600.

Turning now to FIG. 7, illustrated therein is an alternate embodiment ofa light projection source 700 in accordance with embodiments of theinvention. In FIG. 7, the optical feedback component 721 comprises abeam splitter 771 and mirror 772 combination. Beam splitters, well knownto those of ordinary skill in the art, are devices that split a beam oflight into multiple components. In embodiments of the present invention,the beam splitter 771 is configured to split the received beam into afeedback component and a projection component. The beam splitter 771delivers the feedback component, which may be between one and tenpercent of the received collimated light beam, to the mirror 772. Thefeedback component reflects off the mirror 772 and is delivered back tothe laser light sources 761,762,763, thereby causing coherence collapse.The projection component is delivered to the light modulator 703 suchthat images can be formed on a display surface (207). Beam splitters 771suitable for use with the invention can take many forms, including cubedprisms, half-silvered mirrors, and dichroic mirrored prism assemblies.

Turning now to FIG. 8, illustrated therein is one method 800 of reducingspeckle associated with an image presentation on a display surface thatis suitable for use with embodiments of the present invention. At step801, a plurality of light sources produces at least two beams of light.At step 802, one or more optical alignment devices orient the at leasttwo light beams into a collimated beam. At step 803, an optical feedbackdevice separates the collimated beam into a projection component 805 anda feedback component 804. In one embodiment, the projection componentamplitude is between one and ten percent of the amplitude of thecollimated light beam. This step 803 can include the step of disposingthe feedback component between 0.1 millimeters and 100 millimeters awayfrom the laser light sources along an optical axis running from thelaser light sources to the optical feedback device.

At step 806, the optical feedback device delivers the projectioncomponent to a modulation device so that images can be projected to auser at step 807. The modulation device forms the image presentation anddelivers the image presentation to the display surface for viewing. Atstep 808, the optical feedback device delivers the feedback component804 to the laser light sources, thereby causing each of the laser lightsources to operate in a coherence collapsed state at step 809.

Turning now to FIG. 9, illustrated therein are two optional ways step803 of FIG. 8 can be carried out. Specifically, the step 803 ofseparating the collimated beam into the projection component and thefeedback component can comprises either the step 901 of providing apartially reflective mirror or the step 902 of providing a systemcomprising a beam splitter and mirror. It will be clear to those ofordinary skill in the art having the benefit of this disclosure that thesteps of FIG. 9 are illustrative only, as other types of opticalfeedback devices may be supplied in lieu of a partially reflectivemirror or a beam splitter/mirror combination.

Turning now to FIG. 10, illustrated therein is an exemplary applicationfor an imaging system (200) in accordance with embodiments of theinvention. Specifically, imaging systems (200) as set forth herein maybe incorporated into a device 1000. The device 100 may be any of amobile telephone, a portable DVD player, a portable television device, alaptop, a portable e-mail device, a portable music player, a personaldigital assistant, or any combination of the same.

The device 1010 may include a projector 1001 incorporating any one ormore of the foregoing speckle reduction apparatuses and configured toexecute any one or more of the foregoing speckle reduction methods. Theprojector 1001, in one embodiment, is coupled to a processor 1002programmed to control the projector 1001. The projector 1001 includesthe laser light sources (201) and the optical feedback component (221)and other speckle reduction components described herein.

The processor 1002 may be coupled to a memory 1003 storing image data1004, which may include either still image or video data. The processor1002 may be programmed to process the image data to generate controlsignals causing the projector 1001 to create an image corresponding tothe image data 1004 on the display surface 1007. The processor 1007 mayalso be coupled to one or more input and output devices. For example adisplay 1005 may enable a user to view the status of operation of theprocessor 1002 and may serve as an alternative means for displaying theimage data 1004. The processor 1002 may also be coupled to a keypad 1006for receiving user inputs and control instructions.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Thus, while preferred embodiments of the invention havebeen illustrated and described, it is clear that the invention is not solimited. Numerous modifications, changes, variations, substitutions, andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as defined by thefollowing claims. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.

1. A method of reducing speckle associated with an image presentation ona display surface, the method comprising the steps of: producing atleast two beams of light from laser light sources; orienting the atleast two beams of light into a collimated beam; separating thecollimated beam into a projection component and a feedback component;delivering the projection component to a modulation device; anddelivering the feedback component to the laser light sources, therebycausing each of the laser light sources to operate in a coherencecollapsed state.
 2. The method of claim 1, further comprising the stepof causing the modulation device to form the image presentation and todeliver the image presentation to the display surface.
 3. The method ofclaim 1, wherein the feedback component comprises between one and tenpercent of the collimated beam.
 4. The method of claim 1, wherein thestep of separating the collimated beam into the projection component andthe feedback component comprises the steps of providing one of apartially reflective mirror or a system comprising a beam splitter andmirror.
 5. The method of claim 4, wherein the step of separating thecollimated beam into the projection component and the feedback componentcomprises disposing the feedback component between 0.1 millimeters and100 millimeters away from the laser light sources along an optical axisrunning from the laser light sources to the feedback component.